We know: sitting all day at a white collar desk job is killing us, it's worse than smoking. The case has already been made that standing at work can benefit health. Now researchers are showing that a more active alternative could have multiple benefits.

A new study from researchers at the University of Minnesota finds that treadmill desks might not only improve health of office workers but also increase worker productivity.

For one year the authors of the study, published at PLOS ONE, monitored 40 U.S. office workers at a financial services company who voluntarily gave up their office chairs for treadmill desks.

When using the treadmill desks, the employees -- who were able to walk at the desks at up to two miles per hour -- found that they burned 7-8 percent more calories per day than before they began using the treadmill desks.

But the most impressive impact the treadmill desks had on employees was an uptick in productivity. To measure this, the employees and their supervisors regularly completed surveys that asked both to rate the quantity of performance, quality of performance, and quality of interaction with co-workers on a 10-point scale.

"For the duration of the study, productivity increased by close to a point," said Avner Ben-Ner, co-author of the study, in a press release. "That’s a substantial increase."

But the changes in productivity weren't immediate. The researchers found that performance actually declined, as the employees got comfortable with slowly walking while they worked, before gradually increasing over time.

Of course, it's not easy to objectively measure workplace performance and using surveys is certainly a subjective measure. But the fact that workers and supervisors believe they're doing better work has to count for something.

The other limitation to the study is that all the participants were volunteers. According to the report: "volunteers have self-selected into the experiment, and therefore they may have walked more and worked better than other employees would have if assigned to treadmill workstations."

The study also doesn't look at how people with different fitness levels are impacted by treadmill desk or how the impact might change depending on the tasks employees are completing, both of which the researchers suggest for future study.

Looking to make the switch? Danny Sullivan, over at our sister-site CNET, has a good look at his transition to life on the treadmill desk and some of the options available to consumers.